Metal roofing over aging shingles - Correct way to install?

[MMagis]

One problem I am aware of is if the asphalt shingles start burning under the metal roof you can't get water on it. The fire will keep burning/spreading under the metal protected from the water spray. The local firemen do not like metal roofs as they can't get on them easily and safely so they have to change how they approach a fire when it has a metal roof.

Thanks, that makes sense.

 

[JB4310]

I'm a firefighter by trade...
if you install a roof over ANY existing roof you are begging for trouble should your house, barn, shed, etc. catch fire. The "layering" of the roofs will trap the heat in your house, barn, shed, etc.

From a construction perspective...
You are adding more weight to your roof and if you add leaves, snow, etc then your roof could collapse due to the weight. I would always remove the old roofing to avoid future problems; if nothing else to inspect the roof decking for problems.

From a roofer's perspective, until the architectural shingles became so popular, every home or business over 25 years old had 2 layers of roof material on them. Where I live and work that was just about every other home (the homes over 40 to 50 years old had their 2 layers torn off)
Nothing wrong with 2 layers of roofing, and I don't see how another layer of roofing makes much of a difference in the conflagration of fire, at least with asphalt shingles anyway.

As far as weight goes, metal is 1/4 the weight of asphalt shingles, so that is a non issue. As far as fire goes (with metal roof), it may in fact be more difficult to extinguish, I have no experience in that area but from what I've heard some home owners insurance companies give a discount for homes with metal roofs due to it's fire resistance.

JB

 

[tallyho8]

Home Depot metal? I don't know if your Home Depot has better metal but the ones here sell metal so thin you can practically tear it like aluminum foil. Our code requires 26 gauge metal on the roof and I would not consider any less for a home. Lighter gauges will bend as you walk on them and the screws will tear right through as the panels blow off in a storm.

This is my recommendation: It worked great for me. Leave the old shingles on for insulation and sound deadening. Use 2X4s for furring strips instead of 1X4s for 2 reasons. 1. The 1 1/2" screws will hold much better than the 1" screws usually used on 1X4s and the 2X4s are much stronger in a storm. The 2X4s will allow lots of cool air flow for better insulation under the metal when applied as I did.

Buy the 4X8 X3/4" foam insulating panels and attach them to the roof between the furring strips. This leaves 3/4" for air flow. Then attach the metal to the 2X4s. See photo.

After Katrina this is how I did my roof and my attic is 20 degrees cooler in the summer than it was before. The roof is very quiet in a rainstorm. You can not hear rain falling on the metal. I'm sure your Florida weather is similar to our Louisiana weather and the extra insulation pays future dividends. I did this roof completely by myself and pocketed 2/3 of the money the insurance company gave me for the repairs.

 

[Leejohn]

I have been reading everyones post, because I'm getting ready to put a metal roof on. My ? is, why put insulation on the roof and you need ridge vent, roof vent or gable end vents? Seems like I'm missing out on something.
I would think you need the air flow more then anything else.

 

[RoMad]

I love this site because it is such a good place to get tractor advice, but there doesn't seem to be as much knowledge about roofing. :laughing:
I also live in Central Fl. and there are many houses around here, including mine, that have metal roofs put on over shingles. I don't know of any directly on the shingles, they are all on 1x4's put on over the old shingles.
The suggestion I would make is to use galvalume roofing from a reputable dealer. It is much better than the 5V stuff that Home Depot and Lowes sells.
I have bought metal roofing from Gulf Coast Supply in Horseshoe Beach, Tri-County Metal in Trenton and from Metal Roofing of Ocala. Currenty of the three the one in Ocala has the best prices. Metal Roofing in Ocala, Gainesville, Tampa, Orlando - MAKE YOUR FIRST ROOF, YOUR LAST
If you call the guys at Tri-County in Trenton they are very helpful and will recommend the best application for your house.
Good luck

 

[greenthumb]

We put a tampco metal product on about 4 years ago. Has a slate texture look to it. Did the tear off first they did also want to lay over first layer of shingles. My thought was if the roof is supposed to last 50 years plus I don't want old shingles under it. Been happy with them. The only problem is you can't walk on the roof because of the slate look you would dent them. Don't really have a need to be on the roof anyways.

 

[Danny1553]

Speaking from experience...My barn has metal roofing screwed/nailed directly to the original wood shakes. We get some nasty windstorms through here every spring, and every spring, without fail, I've got to go up and nail the roofing back down the best I can (If it hasn't been blown completly off..., I've got three tarps up there now). When I re-roof (Soon!), I am taking it down to the sheathing and starting fresh, screwing directly to the 1" or better thick white oak sheathing boards-this should prevent losing any more roofing. Based on this, IMHO, I would not even consider roofing over old roofing, at least not in Tornado Alley.

Dan

 

[Dallas_Lilly]

When I moved into the house I live in now the insurance company wouldn't write a policy until the roof was replaced I couldn't close until I had a policy, you can see the delima. This was the middle of December 7 years ago, I had two days of sunshine before the snow came again and I didn't feel I had enough time to to strip the 2400 sq roof and get the new metal on before the snow. I made a decision to roof over the shingles and call it good. So far no problems with rust or extra weight. However the climate in AZ is different, nothing rusts! We had a big storm two years ago and had 5 feet of wet snow, flat roofs were collapsing all over town and many people were shoveling roofs. My roof the snow was falling off before I even thought about shoveling. I also get 60 mph winds in the spring and it has never tried to lift. It was a Fabaral from Depot. One thing I did learn is the wood pointed screws with the rubber washers can be cranked down tighter than the self tapping metal screws. Just have to turn up the speed on the drill to get them to go through the metal

 

[beppington]

I also live in Central Fl. and there are many houses around here, including mine, that have metal roofs put on over shingles. I don't know of any directly on the shingles, they are all on 1x4's put on over the old shingles.
The suggestion I would make is to use galvalume roofing from a reputable dealer. It is much better than the 5V stuff that Home Depot and Lowes sells.
I have bought metal roofing from Gulf Coast Supply in Horseshoe Beach, Tri-County Metal in Trenton and from Metal Roofing of Ocala. Currenty of the three the one in Ocala has the best prices. Metal Roofing in Ocala, Gainesville, Tampa, Orlando - MAKE YOUR FIRST ROOF, YOUR LAST
If you call the guys at Tri-County in Trenton they are very helpful and will recommend the best application for your house.
Good luck

Holy cow what a small world!! Just tonight I saw a commercial for Tri-County Metal!!! ... and I jotted their website down! That commercial got me thinking about buying good metal from them & doing the roof myself. After all, I built most of this house myself, with my dad's help, between '90 & '92 ... except shingling the roof. We did all the framing & roof structure up through tar paper, but when it came time to shingle I just couldn't stand the thought of my ankle spending any more time on this 8/12 roof ... & a local contractor charged me $1,000 for installation! :shocked: I could not pass up that deal, & they did a great job :thumbsup: No leaks in 20 years.

Now ... can I stand to be up there this time, to do an entire roof, with 20-year-older joints??? I dunno. But it's killin' me to consider paying someone else to do it when I know I can do the job just right. :laughing:

 

[mmurphy]

Go to bare decking. Put at least 30# felt, and or fanfold depending on your area. The reason for the foam insulation is not to give an R value but to keep condensation from happening. Watch any machine shed in colder climates that are just stick and metal, when it frosts you can point to every purlin in the roof.